Many athletes and non-athletes utilize weight lifting or weight training exercises to build strength and/or bulk, to prevent injury, or to improve overall condition and appearance. Typically, weight training exercises are performed with either exercise machines or free weights, i.e., barbells and weighted plates, dumbbells, etc. For various reasons, most exercise programs incorporate both machines and free weights in a variety of different exercise routines in order to maximize the effect of working out a desired number of muscle groups.
On one hand, free weights offer a number of advantages over exercise machines. For one, they are relatively inexpensive in comparison. Free weights are also more versatile because a variety of exercises can be performed with one set of weights, whereas most exercise machines are designed for only one exercise. For those exercise machines which provide for more than one exercise, cost usually increases proportionately with the number of exercises. Finally, free weights are popular among many weight lifters because the lifting movements are not restricted to prescribed planes of motion and at prescribed angles.
However, there are a number of inherent disadvantages associated with free weights. One such disadvantage relates to safety. Although most weight room instructors strongly advise against an individual working out by himself or herself, this cautionary measure is particularly important when the lifting of free weights is involved. This is due to commonly recognized dangers such as the possibility of dropping a weight on a body part, or becoming trapped beneath a bar, which could easily occur in exercises such as bench press, incline press or squat. Additionally, through carelessness, loading and unloading of heavy weighted plates onto the ends of a bar sometimes results in an unbalanced bar that falls downward from its rack.
Another disadvantage associated with free weights relates to the fact that the weight resistance, or opposing force, that is exercised against is always directed vertically downward by gravity. Yet, the moment arm of the weight about the pivot point varies considerably throughout the full range of motion. This principle is explained in U.S. Pat. No. 3,998,454 with respect to a commonly performed exercise referred to as the dumbbell bicep curl. In short, the applied moment arm about the elbow varies according to the sine of the angle of the lower arm with respect to the vertically oriented upper arm. The moment arm is greatest when the angle is 90.degree., and it is lowest near 180.degree. and 0.degree..
If the resistance capabilities of the muscles of the human body matched this moment arm, the degree of difficulty experienced by the exerciser would be uniform, or balanced, throughout this range of motion. However, as reported in U.S. Pat. No. 3,998,454, the strength generated by the human muscles during this exercise is not in fact "balanced" throughout the range of motion, and there are some "sticking points" of increased difficulty. As a result, maximum benefits are not achieved when performing a bicep curl with a dumbbell.
A pullover machine disclosed in U.S. Pat. No. 3,998,454 utilizes an eccentric cam to vary weight resistance over the range of motion for the muscles utilized in a pullover maneuver. Over the years, for various muscle groups, a number of these cam and chain machines have attempted to match resistance variation through a range of motion with the natural strength curve associated with the human body for those particular muscle groups. To the extent that these machines actually do correctly match resistance variation to the appropriate strength curve, an improvement over lifting of free weights has been achieved.
However, machines of this type suffer from a number of practical disadvantages. For instance, the chains and cams of these machines are susceptible to rust and debris buildup which increases the total amount of resistance against movement of the limb during exercise. Moreover, some of the cam and chain machines employ resistance in the form of permanently connected weight plates that move along a rigid guide. This guide is also susceptible to rust or debris buildup. In order to maintain optimum conditions for these machines, the chains, cams and guides must be lubricated regularly.
In addition to the practical disadvantages associated with maintenance and/or maintenance costs, another disadvantage relates to the fact that these cam and chain machines do not permit the degree of freedom of movement that is possible when lifting free weights. For example, with respect to a muscle group other than the one to which this invention is directed, the pullover machine of U.S. Pat. No. 3,998,454 restricts upper body movement along two parallel, rigidly connected planes, with shoulder pivot about vertically fixed positions. Many exercisers complain that this machine or others like it are simply too confining with respect to the possible freedom of movement for the muscles that are exercised, confining almost to the point of discomfort.
One attempt to solve this problem involves the use of machines that employ weighted levers. With respect to an exercise commonly referred to as a dumbbell press, because it is most often performed with dumbbells, a machine has been designed that utilizes a double handled lever pivotally connected to a frame to effectively work the same muscle group used when performing a seated press with dumbbells. In relation to the respective muscle groups, lever-type machines of this nature permit more degrees of freedom of movement than cam and chain machines such as the pullover machine disclosed in U.S. Pat. No. 3,998,454.
Unfortunately, even this lever-type machine suffers from a subtle disadvantage that most weight lifters apparently have assumed to be inherent with all exercise machines. That is, the planes or angles of prescribed movement do not seem quite right in relation to the musculoskeletal structure of a normal person. In short, this machine and others like it do not seem to "fit" the human body, or simply, they do not feel right. Moreover, some individuals have complained that excessive joint stress may result from use of these machines.
One explanation for this problem is derived from a theory that is based upon accumulated years of observing and analyzing athletic movements of the body in comparison to weight lifting movements. Proponents of this theory point out that most musculoskeletal movements are rather complex and involve multiple joints and multiple degrees of freedom, while most exercise machines are designed to mimic simple movements that are at either right angles or parallel to the body. In a sense, most exercise machines oversimplify the musculoskeletal movements of the human body, and there is room for improvement in the design of exercise machines, particularly when considering that the ultimate objective is to obtain maximum muscular benefit with minimum joint stress.
Finally, although the prior dumbbell press machine known by the inventor may be used to exercise one arm at a time, it was not designed specifically for that purpose. As a result, performance of onehanded exercise on such a machine may even further accentuate the awkwardness that is felt. This significantly limits the practical uses of such machines for the purpose of rehabilitation, where it is often desirable to monitor the relative strength of a previously injured, recovering limb in comparison with a healthy limb.
It is therefore an object of the invention to provide an improved dumbbell press exercise machine that more naturally accommodates the musculoskeletal movements of a person's body.
It is another object of the invention to provide an improved dumbbell press exercise machine that maximizes the exercise benefit attainable during a military press maneuver while minimizing skeletal or joint stress associated therewith.
It is still another object of the invention to provide an improved dumbbell press exercise machine with increased versatility in exercising one arm at a time.